Spark plug electrode



Patented Mar. 20, 1951 UNITED STATES PATENT OFFICE Bayes, Basking Ridge,N. J .assignors to Baker & Company, Inc., Newark, N. J a corporation ofNew Jersey No Drawing. Application January 12, 1949, Serial No. 70,593

3 Claims.

This invention relates to sparkplugs and is concerned more particularlywith sparkplug electrodes.

The construction material of sparkplug electrodes must be a metal havinga suitably high melting point and be a good conductor of heat andelectricity, and must possess a number of other favorablecharacteristicssuch as strength and resistance to erosion in thepresence of the fuel-required for satisfactory performance in operation.

Sparkplug electrodes may consist, therefore, of base metals or preciousmetals. Electrodes of such metals as platinum or alloys thereof are farsuperior to electrodes of base metal such as nickel ortungsten or alloysof such metals, but are too expensive for general use, as, for instance,in internal combustion engines of automobiles, and are, therefore,-restricted in use to more critical uses such as in internal combustionengines of airplanes.

Silver has excellent resistance to corrosion by the fuels of internalcombustion engines and is a good conductor of heat and electricity andin theory would be an excellent construction material for sparking plugelectrodes. Unfortuoately, however, silver which has a melting point ofabout 960 C. is not adapted to withstand the high temperatures, up toabout 800 C. and more, which it would be subjected during the arcing )fthe electrodes, with the result that sparkplug electrodes made of silverdeteriorate fast. The lne grain crystal structure, considerable hard-1855 and tensile strength which characterize :ilver in the cold-workedstate persist only at ow temperatures when silver and silver alloys tresubjected to temperatures in excess of 200 3., graingrowth sets inanclhardness and tensile :trength are lowered, tendencies which becomespecially marked at higher temperatures, in articular at about 800 0.,resulting in ultimate allure of the silver sparkplug electrode at an:arly state, and erosion under the corrosive inluence of the vaporizedfuel at elevated temlerature is quite. rapid. Another disadvantage fsilver, and its alloys, is that sparkplug elecrodes must be cleaned fromtime to time and ilver, .after having been exposed to elevatedtemeratures, is not sufiiciently hard to withstand he .blast of thecustomarily used sand blast lethod.

It is one object of this invention to produce a parkplug electrode whichshall have highelecrical conductivity and high heat conductivity. isanother object of this invention to provide such a sparkplug electrodeof silver. It is a further object of this invention to produce a silversparkplug electrode which shall be capable of operating at elevatedtemperatures and which shall have substantial hardness and ability toretain a high degree of hardness at elevated temperatures even in excessof 800 C. Other objects and advantages of our invention will appear fromthe description thereof hereinafter follow- Sparkplugs and thearrangement of the elecrodes therein, such e. g. as a center electrodeprovided within a mass of insulation material, with or Without a metalcore, in operative position with a side electrode secured to a metalshell, or other arrangements, are well known in the art and ourinvention is not concerned with such structural features or arrangement,but is concerned merely with the metal or metal composition of which theelectrode, or at least one electrode such as the center electrode,consists.

This application is a continuation-in-part of our co-pendingapplication, Serial No. 691,170, filed August 16, 1946, now abandoned.

The electrode of the present invention is formed of silver and alloys ofsilver, e. g. with copper, in the form of a compacted heated, i. e.sintered, mass containing a refractory oxide distributed uniformly andin fine divided state throughout the mass of silver along the crystalboundaries of such silver and silver alloys.

The refractory oxide may be any one or more of the oxides commonly knownas refractory oxides, including oxides of the alkaline earth metals ofgroup II a of the periodic table, e. g. beryllium, strontium, barium, orof metals of group III I) of the periodic table, e. .g. aluminum,scandium, yttrium and rare earth metals (Atomic Nos. 57-71) e, g.lanthanum, cerium or neodymium, or of metals of group IV D of theperiodic table, e. g. zirconium, thorium, or of metals of group V b ofthe periodic table, e. g. vanadium or colombium, or the sesquioxide ofchromium in group VI b of the periodic table. The enumeration of thespecific refractory oxides above referred to is illustrative ofrefractory oxides but is not meant to exclude other oxides commonlyincluded in the term refractory oxide.

Among the refractory oxides we have found that the most suitable onesare the oxides of thorium, beryllium and aluminum.

The constituents of the mass are provided in finely. divided conditionwhich may be produced in any suitable manner. Thus, the silver oralloying metal may b provided, for instance, by

3 mechanical disintegration, granulation or the like, or by chemicalmeans such as by precipitation or by decomposition and reduction ofmetal compounds. The refractory oxide may be provided, for instance, inthe form of dry powder or paste or in the form of a solution of a saltadapted to be decomposed to the oxide by heating. The con- I stituentsare mixed in such finely divided condition, i. e. either in their finalform of metal and oxide, respectively, or in any of the preparatoryphases or in the final form of one constituent, e. g. solution of silvercompound with solution of salt adapted to be decomposed to the oxide orwith refractory oxide, or otherwise.

The mixture is then subjected to heat durin or after the compactingprocess, as by hot pressing or by pressing and sintering, whereafter thecompacted mass can be worked, as by swaging, rolling, drawing and soforth, to form the mass into the desired shape, such as, for instance,wire which may then be converted into the desired shape, such as wire,used to form the sparkplug electrode. In order to obtain best results,the material should be hard worked to give the silver a highly fibrousstructure.

The amount of refractory oxides may be as low as 0.01% or as high as10%, but in order to retain without substantial impairment the highelectrical and heat conductivity of the silver, while yet obtaining theretention of the fin or fibrous crystal structure on continuous exposureto elevated temperatures, e. g. 800 C., and conveying to the silver aspecial hardness, the content of refractory oxide should not exceedabout 1.5%. Hence, we prefer to use from about 0.1% to 1% refractoryoxide in the silver sparkplug electrodes of this invention, with 3% to5% generally as the maximum limit.

The following example will illustrate one suitable and advantageousmethod of producing the improved silver according to the invention. 622grams silver powder were covered with distilled water to make a heavypaste. 6.23 grams &

tal structure, characteristic of cold worked fine silver at lowertemperatures. The tensile strength and hardness of the electrodematerial are far greater than the tensile strength and hardness ofsilver as such at such elevated temperatures. For instance, referring tothe specific example hereinabove stated, the wire when annealed at 70.060 inch for 30 minutes at 550 F. shows a thorium oxide were added inthe form of thorium nitrate. The materials were mixed and the mixturestirred while drying over a water bath. The mixture was finally driedcompletely at 180 C. The dry powder mixture passed through a 100 meshsieve. The powder mixture was then pressed into a bar, 4 x 1" x 1", forinstance at 12.5 tons pressure per square inch and was then sintered forapproximately one hour at 800 C. to 900 C., during which process thematerial is converted into a compacted finely grained crystallinestructure and the thorium nitrate becomes decomposed to thorium oxide.The sintered bar was then swaged with intermediate anneals down to .300and cold worked from thereon.

The refractory oxide is distributed throughout the silver mass of theelectrode, along the boundaries of the silver crystals. Care'is,therefore, taken, as to the temperature of processing the material and,where necessary, as to avoidance of reducing conditions, that therefractory oxide is not decomposed to metal, since in the metallicstate, as distinguished from the oxide state, the material would alloywith the silver.

The silver sparkplug electrodes of this invention withstand the hightemperatures occurring in the continuous arcing operation.Recrystallization of the silver, and consequent deterioration, isresisted, so that erosion in the presence of the fuel vapors issubstantially avoided. Even at 850 C. and more, the silver retains afine crys- Rockwell hardness of 15 T l0 against a Rockwell hardness of15 T 30 for regular fine silver, that is the silver of our electrode hasa hardness onethird greater at such temperatur than fine silver.

One interesting characteristic of the electrodes of the invention istheir uniformity of wear, or erosion, as distinguished from theirregular erosion of other types of electrodes. In the conventionalnickel alloy sparkplug electrode used in automotive internal combustionengines, such as nickel alloy electrodes, the center electrodes areeroded faster at the corners, leaving a conically shaped end. In theelectrodes of the invention, the wear across the end of the electrode isuniform and the customary initially fiat surface of the center electrodeis maintained substantially uniform, so that the initial configurationis retained intact, thus contributing further to increased life andefficient operation of these electrodes.

sparkplug electrodes, i. e. the center electrode as well as the earthedside electrode or electrodes, in accordance with our invention, exhibita much longer useful life than like electrodes of regular silver. Theypossess the low electrical resistivity and high resistance to oxidationand corrosion which are characteristic of fine silver but also possessfine crystal grain structure and great hardness and strength at elevatedtemperatures, characteristics not heretofore exhibited by silversparkplug electrodes. The electrodes are thus more efficient and longlived and, furthermore, are capable of being cleaned by the customarysand blasting method. The additional favorable properties thus possessedby sparkplug electrodes in accordance with this invention make itpossible to utilize such silver sparkplug electrodes .where heretoforeit was thought impossible to use such electrodes.

The invention is, of course, applicable to electrodes of alloys ofsilver, i. e. alloys containing a major proportion of silver and a minorproportion of other suitable alloying elements which may be taken fromthe group of precious metals, for instance gold or platinum groupmetals, e. g. platinum, palladium and ruthenium or the like, or from thegroup of base metals, for instance copper, although, in general, theadmixtures of such other alloying elements should not exceed about 20%of the silver content. The term silver as used in the appended claimsshall include such silver alloys, and the term refractory ox-' ide asused in the appended claims shall mean one or more refractory oxides.

While theelectrode consisting of the sinterec' mixture will normally beof wire or the like composed in its entirety of the mixture specified,we do mean to include also structures in which 131 arcing surface bodyis composed of such mixtures or where the compacted heated mixture 0:silver and refractory oxide described forms the core of the electrodesurrounded by an integra shell of silver, or other suitable metal.

What we claim is:

1. A spark plug comprising a pair of electrode electrically insulatedfrom each other and a least one electrode formed of a compacted heatermixture of silver and refractory oxide, the constituents being initiallyin finely divided condition, wherein the refractory oxide is distributedthroughout the body of said silver along the grain boundaries of thecrystals thereof, said refractory oxide constituting from 0.01% to 1.5%of said mixture.

2. A spark plug comprising a pair of electrodes electrically insulatedfrom each other and formed of a sintered material of silver and thoriumoxide, the constituents being initially in finely divided conditionwherein said thorium oxide is distributed throughout the body of saidsilver along the grain boundaries of the crystals thereof, said thoriumoxide constituting from 0.01% to 10% of said material.

3. A spark plug comprising a pair of electrodes electrically insulatedfrom each other and formed of a sintered material of silver and aluminumoxide, the constituents being initially in finely divided conditionwherein said aluminum oxide is distributed throughout the body of saidsilver along the grain boundaries of the crystals thereof, said aluminumoxide constituting from 0.01% to 10% of said material.

MAX JOSEPH STUMBOCK.

ROSS BAYES.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,200,854 Ruben May 14, 1940"2,265,352 Corbin et al Dec. 9, 1941 7 2,396,101 Hensel et al Mar. 5,1946 2,406,172 Smithells Aug. 20, 1946

